Frame transmitting method and frame receiving method

ABSTRACT

A method of transmitting a frame is provided by a device in a WLAN. The device sets as additional data subcarriers some of subcarriers which are not set as data subcarriers in at least part of fields included in a frame of a legacy frame format, and allocates information to the additional data subcarriers.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 15/626,966,filed on Jun. 19, 2017, now U.S. Pat. No. 10,326,618, issued Jun. 18,2019, which is a continuation of application Ser. No. 14/684,117, filedon Apr. 10, 2015, now U.S. Pat. No. 9,712,342, issued Jul. 18,2017,_which claims the benefit of U.S. Provisional Application No.61/978,776, filed on Apr. 11, 2014 in the U.S. Patent and TrademarkOffice and priority to and the benefit of Korean Patent Application No.10-2015-0047099, filed on Apr. 2, 2015 in the Korean IntellectualProperty Office, the entire contents of which are incorporated herein byreference.

BACKGROUND (a) Field

The described technology relates generally to a frame transmittingmethod and a frame receiving method. More particularly, the describedtechnology relates generally to a frame transmitting method and a framereceiving method in a wireless local area network (WLAN).

(b) Description of the Related Art

A WLAN is being standardized by the IEEE (Institute of Electrical andElectronics Engineers) Part 11 under the name of “Wireless LAN MediumAccess Control (MAC) and Physical Layer (PHY) Specifications.” After anoriginal standard was published on 1999, new version standards arecontinuously published by amendments. The IEEE standard 802.11a (IEEEStd 802.11a-1999) supporting 2. 4 GHz band was published on 1999, andthe IEEE standard 802.11g (IEEE Std 802.11g-2003) supporting 5 GHz bandwas published on 2003. These standards are called legacy. Subsequently,the IEEE standard 802.11n (IEEE Std 802.11n-2009) for enhancements forhigher throughput (HT) was published on 2009, and the IEEE standard802.11ac (IEEE 802.11ac-2013) for enhancements for very high throughput(VHT) was published on 2013. Recently, a high efficiency WLAN (HEW) forenhancing the system throughput in high density scenarios is beingdeveloped by the IEEE 802.11ax task group.

In a new version WLAN, signaling information with which a transmittingdevice provides a receiving device may be increased compared with theprevious WLAN. In this case, a scheme for providing additional signalinginformation with maintaining the backward compatibility with theprevious WLAN is required.

SUMMARY

An embodiment of the present invention provides a frame transmittingmethod and a frame receiving method for providing additional signalinginformation with maintaining the backward compatibility with theprevious WLAN.

According to another embodiment of the present invention, a method oftransmitting a frame is provided by a device in a WLAN. The methodincludes generating a legacy short training field, a legacy longtraining field, a legacy signal field, and a data field of a legacyframe format, allocating predetermined information to additional datasubcarriers that are some of subcarriers which are not set as datasubcarriers at the legacy frame format, in at least one field among thelegacy short training field, the legacy long training field, the legacysignal field, and the data field, and transmitting a frame including thelegacy short training field, the legacy long training field, the legacysignal field, the data field, and the predetermined information.

The at least one field may include the data field.

The at least one field may further include the legacy signal field.

The additional data subcarriers may include some of subcarriers that areused as guards in the legacy frame format.

The additional data subcarriers may include subcarriers whose indices−28, −27, 27, and 28 on a 20 MHz bandwidth basis.

The additional data subcarriers on a symbol of a plurality of symbolincluded in the at least one field may be used as a long training fieldfor channel estimation.

When M additional data subcarriers are used in each of N symbols of theat least one field, the predetermined information may be allocated by apredetermined M×N matrix pattern.

The frame may be a request to send (RTS) frame or a clear to send (CTS)frame.

The predetermined information may include information on a bandwidthwhich the device uses.

The frame may further include an indication indicating whether the frameis in a mode using an additional data subcarrier.

A predetermined bit of the legacy signal field may include theindication.

A predetermined bit of the first 7 bits in a scrambling sequence forscrambling the data field may include the indication.

The data field may include a service field, and the first 7 bits of theservice field may correspond to the first 7 bits of a scramblingsequence. A predetermined bit of the first 7 bits in the scramblingsequence may include the indication.

The data field may include a service field, and a predetermined bit ofthe eighth to sixteenth bits in the service field may include theindication.

According to yet another embodiment of the present invention, a frametransmitting apparatus of a device is provided in a WLAN. The frametransmitting apparatus includes a processor and a transceiver. Theprocessor generates a legacy short training field, a legacy longtraining field, a legacy signal field, and a data field of a legacyframe format. The processor allocates predetermined information toadditional data subcarriers that are some of subcarriers which are notset as data subcarriers at the legacy frame format, in at least onefield among the legacy short training field, the legacy long trainingfield, the legacy signal field, and the data field. The transceivertransmits a frame including the legacy short training field, the legacylong training field, the legacy signal field, the data field, and thepredetermined information.

According to still another embodiment of the present invention, a methodof receiving a frame is provided by a device in a wireless communicationnetwork. The method includes receiving a frame of a legacy frame formatincluding a legacy short training field, a legacy long training field, alegacy signal field, and a data field, and acquiring information fromadditional data subcarriers that are set by some of subcarriers whichare not set as data subcarriers at the legacy frame format, in at leastone field among the legacy short training field, the legacy longtraining field, the legacy signal field, and the data field.

The additional data subcarriers may include some of subcarriers that areused as guards in the legacy frame format.

The additional data subcarriers may include subcarriers whose indices−28, −27, 27, and 28 on a 20 MHz bandwidth basis.

The information may include information on a bandwidth which a devicetransmitting the frame uses.

The method may further include determining whether the frame is in amode using an additional data subcarrier, based on an indicationincluded in a predetermined bit of the frame.

The method may further include determining whether the frame is in amode using an additional data subcarrier, by measuring a power ofsubcarriers that are not set as data subcarriers in the legacy frameformat.

According to further embodiment of the present invention, a frametransmitting apparatus of a device is provided in a WLAN. The frametransmitting apparatus includes a processor and a transceiver. Thetransceiver receives a frame of a legacy frame format including a legacyshort training field, a legacy long training field, a legacy signalfield, and a data field. The processor acquires information fromadditional data subcarriers that are set by some of subcarriers whichare not set as data subcarriers at the legacy frame format, in at leastone field among the legacy short training field, the legacy longtraining field, the legacy signal field, and the data field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram exemplifying a WLAN device.

FIG. 2 is a schematic block diagram exemplifying a transmitting signalprocessor in a WLAN.

FIG. 3 is a schematic block diagram exemplifying a receiving signalprocessing unit in the WLAN.

FIG. 4 exemplifies IFS relationships.

FIG. 5 is a schematic diagram explaining CSMA/CA based frametransmission procedure for avoiding collision between frames in achannel.

FIG. 6 exemplifies a frame format in a wireless communication networkaccording to an embodiment of the present invention.

FIG. 7 exemplifies a subcarrier allocation of a 20 MHz transmission modein a previous WLAN.

FIG. 8 exemplifies a subcarrier allocation in a wireless communicationnetwork according to an embodiment of the present invention.

FIG. 9, FIG. 10, and FIG. 11 exemplify a frame format in a wirelesscommunication network according to various embodiments of the presentinvention.

FIG. 12, FIG. 13, FIG. 14, and FIG. 15 exemplify a method for detectinga frame format in a wireless communication network according to variousembodiments of the present invention.

FIG. 16 and FIG. 17 exemplify a frame format at a multi-bandwidth in awireless communication network according to various embodiments of thepresent invention.

FIG. 18 shows an example of a channel width used in a wirelesscommunication network according to an embodiment of the presentinvention.

FIG. 19 and FIG. 20 are drawings explaining an exchange of an RTS frameand a CTS frame in a wireless communication network according to anembodiment of the present invention.

FIG. 21 is a flowchart exemplifying a frame transmitting method in adevice of a wireless communication network according to an embodiment ofthe present invention.

FIG. 22 is a flowchart exemplifying a frame receiving method in a deviceof a wireless communication network according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, only certain embodiments of thepresent invention have been shown and described, simply by way ofillustration. As those skilled in the art would realize, the describedembodiments may be modified in various different ways, all withoutdeparting from the spirit or scope of the present invention.Accordingly, the drawings and description are to be regarded asillustrative in nature and not restrictive. Like reference numeralsdesignate like elements throughout the specification.

In a wireless local area network (WLAN), a basic service set (BSS)includes a plurality of WLAN devices. The WLAN device may include amedium access control (MAC) layer and a physical (PHY) layer accordingto the IEEE (Institute of Electrical and Electronics Engineers) standard802.11. The plurality of WLAN devices may include a WLAN device that isan access point and the other WLAN devices that are non-AP stations(non-AP STAs). Alternatively, all the plurality of WLAN devices may benon-AP STAs in Ad-hoc networking. In general, the AP STA and the non-APSTA may be collectively called the STA. However, for easy description,only the non-AP STA may be called the STA.

FIG. 1 is a schematic block diagram exemplifying a WLAN device.

Referring to FIG. 1, the WLAN device 1 includes a baseband processor 10,a radio frequency (RF) transceiver 20, an antenna unit 30, a memory 40,an input interface unit 50, an output interface unit 60, and a bus 70.

The baseband processor 10 performs baseband signal processing, andincludes a MAC processor 11 and a PHY processor 15.

In one embodiment, the MAC processor 11 may include a MAC softwareprocessing unit 12 and a MAC hardware processing unit 13. The memory 40may store software (hereinafter referred to as “MAC software”) includingat least some functions of the MAC layer. The MAC software processingunit 12 executes the MAC software to implement the some functions of theMAC layer, and the MAC hardware processing unit 13 may implementremaining functions of the MAC layer as hardware (hereinafter referredto “MAC hardware”). However, the MAC processor 11 is not limited tothis.

The PHY processor 15 includes a transmitting signal processing unit 100and a receiving signal processing unit 200.

The baseband processor 10, the memory 40, the input interface unit 50,and the output interface unit 60 may communicate with each other via thebus 70.

The RF transceiver 20 includes an RF transmitter 21 and an RF receiver22.

The memory 40 may further store an operating system and applications.The input interface unit 50 receives information from a user, and theoutput interface unit 60 outputs information to the user.

The antenna unit 30 includes one or more antennas. When multiple-inputmultiple-output (MIMO) or multi-user MIMO (MU-MIMO) is used, the antennaunit 30 may include a plurality of antennas.

FIG. 2 is a schematic block diagram exemplifying a transmitting signalprocessor in a WLAN.

Referring to FIG. 2, a transmitting signal processing unit 100 includesan encoder 110, an interleaver 120, a mapper 130, an inverse Fouriertransformer (IFT) 140, and a guard interval (GI) inserter 150.

The encoder 110 encodes input data. For example, the encoder 100 may bea forward error correction (FEC) encoder. The FEC encoder may include abinary convolutional code (BCC) encoder followed by a puncturing device,or may include a low-density parity-check (LDPC) encoder.

The transmitting signal processing unit 100 may further include ascrambler for scrambling the input data before the encoding to reducethe probability of long sequences of 0 s or 1 s. If BCC encoding is usedin the encoder, the transmitting signal processing unit 100 may furtherinclude an encoder parser for demultiplexing the scrambled bits among aplurality of BCC encoders. If LDPC encoding is used in the encoder, thetransmitting signal processing unit 100 may not use the encoder parser.

The interleaver 120 interleaves the bits of each stream output from theencoder to change order of bits. Interleaving may be applied only whenBCC encoding is used. The mapper 130 maps the sequence of bits outputfrom the interleaver to constellation points. If the LDPC encoding isused in the encoder, the mapper 130 may further perform LDPC tonemapping besides the constellation mapping.

When the MIMO or the MU-MIMO is used, the transmitting signal processingunit 100 may use a plurality of interleavers 120 and a plurality ofmappers corresponding to the number of N_(SS) of spatial streams. Inthis case, the transmitting signal processing unit 100 may furtherinclude a stream parser for dividing outputs of the BCC encoders or theLDPC encoder into blocks that are sent to different interleavers 120 ormappers 130. The transmitting signal processing unit 100 may furtherinclude a space-time block code (STBC) encoder for spreading theconstellation points from the N_(SS) spatial streams into N_(STS)space-time streams and a spatial mapper for mapping the space-timestreams to transmit chains. The spatial mapper may use direct mapping,spatial expansion, or beamforming.

The IFT 140 converts a block of the constellation points output from themapper 130 or the spatial mapper to a time domain block (i.e., a symbol)by using an inverse discrete Fourier transform (IDFT) or an inverse fastFourier transform (IFFT). If the STBC encoder and the spatial mapper areused, the inverse Fourier transformer 140 may be provided for eachtransmit chain.

When the MIMO or the MU-MIMO is used, the transmitting signal processingunit 100 may insert cyclic shift diversities (CSDs) to preventunintentional beamforming. The CSD insertion may occur before or afterthe inverse Fourier transform. The CSD may be specified per transmitchain or may be specified per space-time stream. Alternatively, the CSDmay be applied as a part of the spatial mapper.

When the MU-MIMO is used, some blocks before the spatial mapper may beprovided for each user.

The GI inserter 150 prepends a GI to the symbol. The transmitting signalprocessing unit 100 may optionally perform windowing to smooth edges ofeach symbol after inserting the GI. The RF transmitter 21 converts thesymbols into an RF signal and transmits the RF signal via the antennaunit 30. When the MIMO or the MU-MIMO is used, the GI inserter 150 andthe RF transmitter 21 may be provided for each transmit chain.

FIG. 3 is a schematic block diagram exemplifying a receiving signalprocessing unit in the WLAN.

Referring to FIG. 3, a receiving signal processing unit 200 includes aGI remover 220, a Fourier transformer (FT) 230, a demapper 240, adeinterleaver 250, and a decoder 260.

An RF receiver 22 receives an RF signal via the antenna unit 30 andconverts the RF signal into the symbols. The GI remover 220 removes theGI from the symbol. When the MIMO or the MU-MIMO is used, the RFreceiver 22 and the GI remover 220 may be provided for each receivechain.

The FT 230 converts the symbol (i.e., the time domain block) into ablock of the constellation points by using a discrete Fourier transform(DFT) or a fast Fourier transform (FFT). The Fourier transformer 230 maybe provided for each receive chain.

When the MIMO or the MU-MIMO is used, the receiving signal processingunit 200 may a spatial demapper for converting the Fourier transformedreceiver chains to constellation points of the space-time streams, andan STBC decoder for despreading the constellation points from thespace-time streams into the spatial streams.

The demapper 240 demaps the constellation points output from the Fouriertransformer 230 or the STBC decoder to the bit streams. If the LDPCencoding is used, the demapper 240 may further perform LDPC tonedemapping before the constellation demapping. The deinterleaver 250deinterleaves the bits of each stream output from the demapper 240.Deinterleaving may be applied only when BCC encoding is used.

When the MIMO or the MU-MIMO is used, the receiving signal processingunit 200 may use a plurality of demappers 240 and a plurality ofdeinterleavers 250 corresponding to the number of spatial streams. Inthis case, the receiving signal processing unit 200 may further includea stream deparser for combining the streams output from thedeinterleavers 250.

The decoder 260 decodes the streams output from the deinterleaver 250 orthe stream deparser. For example, the decoder 100 may be an FEC decoder.The FEC decoder may include a BCC decoder or an LDPC decoder. Thereceiving signal processing unit 200 may further include a descramblerfor descrambling the decoded data. If BCC decoding is used in thedecoder, the receiving signal processing unit 200 may further include anencoder deparser for multiplexing the data decoded by a plurality of BCCdecoders. If LDPC decoding is used in the decoder, the receiving signalprocessing unit 100 may not use the encoder deparser.

FIG. 4 exemplifies interframe space (IFS) relationships.

A data frame, a control frame, or a management frame may be exchangedbetween WLAN devices.

The data frame is used for transmission of data forwarded to a higherlayer. The WLAN device transmits the data frame after performing backoffif a distributed coordination function IFS (DIFS) has elapsed from atime when the medium has been idle. The management frame is used forexchanging management information which is not forwarded to the higherlayer. Subtype frames of the management frame include a beacon frame, anassociation request/response frame, a probe request/response frame, andan authentication request/response frame. The control frame is used forcontrolling access to the medium. Subtype frames of the control frameinclude a request to send (RTS) frame, a clear to send (CTS) frame, andan acknowledgement (ACK) frame. In the case that the control frame isnot a response frame of the other frame, the WLAN device transmits thecontrol frame after performing backoff if the DIFS has elapsed. In thecase that the control frame is the response frame of the other frame,the WLAN device transmits the control frame without performing backoffif a short IFS (SIFS) has elapsed. The type and subtype of frame may beidentified by a type field and a subtype field in a frame control field.

On the other hand, a Quality of Service (QoS) STA may transmit the frameafter performing backoff if an arbitration IFS (AIFS) for accesscategory (AC), i.e., AIFS[AC], has elapsed. In this case, the dataframe, the management frame, or the control frame which is not theresponse frame may use the AIFC[AC].

FIG. 5 is a schematic diagram explaining a CSMA (carrier sense multipleaccess)/CA (collision avoidance) based frame transmission procedure foravoiding collision between frames in a channel.

Referring to FIG. 5, STA1 is a transmit WLAN device for transmittingdata, STA2 is a receive WLAN device for receiving the data, and STA3 isa WLAN device which may be located at an area where a frame transmittedfrom the STA1 and/or a frame transmitted from the STA2 can be receivedby the WLAN device.

The STA1 may determine whether the channel is busy by carrier sensing.The STA1 may determine the channel occupation based on an energy levelon the channel or correlation of signals in the channel, or maydetermine the channel occupation by using a network allocation vector(NAV) timer.

When determining that the channel is not used by other devices duringDIFS (that is, the channel is idle), the STA1 may transmit an RTS frameto the STA2 after performing backoff. Upon receiving the RTS frame, theSTA2 may transmit a CTS frame as a response of the CTS frame after SIFS.

When the STA3 receives the RTS frame, it may set the NAV timer for atransmission duration of subsequently transmitted frames (for example, aduration of SIFS+CTS frame duration+SIFS+data frame duration+SIFS+ACKframe duration) by using duration information included in the RTS frame.When the STA3 receives the CTS frame, it may set the NAV timer for atransmission duration of subsequently transmitted frames (for example, aduration of SIFS+data frame duration+SIFS+ACK frame duration) by usingduration information included in the RTS frame. Upon receiving a newframe before the NAV timer expires, the STA3 may update the NAV timer byusing duration information included in the new frame. The STA3 does notattempt to access the channel until the NAV timer expires.

When the STA1 receives the CTS frame from the STA2, it may transmit adata frame to the STA2 after SIFS elapses from a time when the CTS framehas been completely received. Upon successfully receiving the dataframe, the STA2 may transmit an ACK frame as a response of the dataframe after SIFS elapses.

When the NAV timer expires, the STA3 may determine whether the channelis busy by the carrier sensing. Upon determining that the channel is notused by the other devices during DIFS after the NAV timer has expired,the STA3 may attempt the channel access after a contention windowaccording to random backoff elapses.

Now, a signaling method in a wireless communication network according tovarious embodiments of the present invention is described with referenceto the drawings. The wireless communication network according to variousembodiments of the present invention may be a WLAN. Particularly, thewireless communication network according to various embodiments of thepresent invention may be a high efficiency WLAN (HEW) that is beingdeveloped by the IEEE 802.11ax task group among WLANs. Hereinafter, thewireless communication network according to various embodiments of thepresent invention is assumed as the WLAN, particularly the HEW, forconvenience.

FIG. 6 exemplifies a frame format in a wireless communication networkaccording to an embodiment of the present invention, FIG. 7 exemplifiesa subcarrier allocation of a 20 MHz transmission mode in a previousWLAN, and FIG. 8 exemplifies a subcarrier allocation in a wirelesscommunication network according to an embodiment of the presentinvention. It is assumed that the frame shown in FIG. 6 is a PHY frame,for example a physical layer convergence procedure (PLCP) frame and usesa channel with a basic bandwidth (for example, 20 MHz bandwidth).Further, the frame shown in FIG. 6 may be a request frame or a responseframe on the request frame. An example of the request frame may be anRTS frame, and an example of the response frame may be a CTS frame.

Referring to FIG. 6, a frame includes a legacy short training field(L-STF), a legacy long training field (L-LTF), a legacy signal field(L-SIG), and a data field. The L-STF and the L-LTF may be used forsynchronization and channel estimation. The L-SIG may include rate andlength information of the data field. The L-STF and the L-LTF eachinclude two symbols, i.e., orthogonal frequency division multiplexing(OFDM) symbols, and the L-SIG includes one symbol. The data field mayinclude a service field, a MAC frame part, and tail bits, and mayfurther include, if necessary, pad bits. As such, the request frame orresponse frame uses a legacy frame format defined in the legacy (IEEE802.11a or IEEE 802.11g) WLAN for the backward compatibility with theprevious WLAN.

In an embodiment of the present invention, among a plurality ofsubcarriers included in each symbol of the data field, M subcarriers areused as additional data subcarriers for carrying signaling informationbesides subcarriers that are allocated to data subcarriers in theprevious WLAN. Here, M is an integer greater than or equal to one.

The number of subcarriers included in one symbol is determined by a sizeof a fast Fourier transform (FFT) that is used. As described above, therequest frame or response frame uses the legacy frame format. In thelegacy frame format, when an inverse Fourier transformer (140 of FIG. 2)of the transmitting device performs an inverse Fourier transform, 64 FFTis used on a 20 MHz bandwidth basis. Accordingly, one symbol of theframe shown in FIG. 6 includes 64 subcarriers. In the legacy frameformat, 64 subcarriers include one subcarrier used as a DC (directcurrent) subcarrier, four subcarriers used as pilots, and elevensubcarriers used as guards. Accordingly, 48 subcarriers among the 64subcarriers are used as data subcarriers. As exemplified in FIG. 7, whena subcarrier index of the DC is 0, tones whose subcarrier indices are−21, −7, 7, and 21 may be used as the pilots, and some tones (i.e.,tones whose subcarrier indices are −32 to −27 and 27 to 31) of both endswith the DC as the center may be used as the guards.

In some embodiments, as shown in FIG. 8, negative subcarriers whoseindices are −28 and −27 and positive subcarriers whose indices are 27and 28 among the 64 subcarriers may be used as the additional datasubcarriers in replace of the guards among the 64 subcarriers.Accordingly, four subcarriers in one symbol can be used as theadditional data subcarriers. In another embodiment, M subcarrier, whereM is different from four, may be used as the additional datasubcarriers.

As described above, since subcarriers which have not been used as thedata subcarrier in the previous WLAN are used as the additional datasubcarrier in the data field of the request frame or response frame,signaling information can be carried through the additional datasubcarriers.

Since the additional data subcarriers correspond to the guards of theprevious WLAN, the previous WLAN device, for example a legacy device, anHT device, or a VTH device determines the additional data subcarrier asthe guards and does not demodulate or use the additional datasubcarriers. However, a HEW device can determine the additional datasubcarriers as the data subcarriers and interpret the additional datasubcarriers. Accordingly, additional signaling information can betransmitted with maintaining the backward compatibility with theprevious WLAN.

FIG. 9, FIG. 10, and FIG. 11 exemplify a frame format in a wirelesscommunication network according to other embodiments of the presentinvention.

Referring to FIG. 9, in some embodiments, additional data subcarriersmay be used in the L-SIG as well as the data field. Then, the additionaldata subcarriers corresponding to the L-SIG, i.e., one symbol can beadditionally used.

In another embodiment, the additional data subcarriers may not be usedin the data field and may be used only in the L-SIG. In yet anotherembodiment, the additional data subcarriers may be used in at least partof the L-STF, the L-LTF, the L-SIG, and the data field.

Referring to FIG. 10, in some embodiments, a transmitting device maycode and modulate information that is transferred by additional datasubcarriers in the same manner as information that is transferred byother data subcarriers. In this case, a part of the additional datasubcarriers may be used as a long training field (LTF) for channelestimation on the additional data subcarriers. For example, theadditional data subcarriers corresponding to two symbols may be used asthe LTF for the channel estimation like the L-LTF.

Accordingly, a receiving device can estimate a channel corresponding tothe additional data subcarriers based on the LTF.

Referring to FIG. 11, in some embodiments, signaling information that istransferred by additional data subcarriers may be provided in a form ofpredetermined pattern. For example, when additional data subcarriers areused in N symbols and four subcarriers are assigned to the additionaldata subcarriers in one symbol, the signaling information may betransmitted in a pattern of 4×N matrix. For example, patterns of apredetermined number may be defined, and each pattern may be assignedpredetermined information. Accordingly, a receiving device can acquireinformation provided by the transmitting device, based on the patternformed by the 4×N matrix that is defined by the additional datasubcarriers of the received frame.

For example, the patterns of the predetermined number may be defined byusing 1 and −1 as in Equation 1. Alternatively, the patterns of thepredetermined number may be defined by using j and −j.

$\begin{matrix}{\begin{Bmatrix}1 & 1 & 1 & 1 & \ldots & 1 & 1 \\1 & 1 & 1 & 1 & \ldots & 1 & 1 \\1 & 1 & 1 & 1 & \ldots & 1 & 1 \\1 & 1 & 1 & 1 & \ldots & 1 & 1\end{Bmatrix},\begin{Bmatrix}1 & {- 1} & 1 & {- 1} & \ldots & 1 & {- 1} \\1 & 1 & 1 & 1 & \ldots & 1 & 1 \\1 & {- 1} & 1 & {- 1} & \ldots & 1 & {- 1} \\1 & 1 & 1 & 1 & \ldots & 1 & 1\end{Bmatrix},{\ldots\;{\quad\mspace{11mu}\begin{Bmatrix}1 & 1 & {- 1} & {- 1} & \ldots & {- 1} & {- 1} \\1 & 1 & 1 & 1 & \ldots & 1 & 1 \\1 & 1 & 1 & 1 & \ldots & 1 & 1 \\1 & {- 1} & 1 & {- 1} & \ldots & 1 & {- 1}\end{Bmatrix}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

In some embodiments, matrix patterns of a predetermined number, forexample four matrix patterns which have the greatest difference inFrobenius norm from among various matrix patterns may be used.

As such, when the signaling information to be transferred by theadditional data subcarriers is provided by the predetermined pattern,the receiving device can interpret the signaling information even iffailing to estimate the channel. Further, even though the transmittingdevice transmits the signaling information on the additional datasubcarriers without coding and/or modulating the signaling information,the receiving device can interpret the signaling information based onthe pattern.

Next, a method where a transmitting device notifies whether a frame istransmitted by using additional data subcarriers is described.

FIG. 12, FIG. 13, FIG. 14, and FIG. 15 exemplify a method for detectinga frame format in a wireless communication network according to variousembodiments of the present invention.

Referring to FIG. 12, an L-SIG includes a rate field, a reserved bit,and a length field. The rate field has 4 bits and the length field has12 bits. A pad bit of 1 bit and tail bits of 6 bits are added after thelength field. In some embodiments, the reserved 1 bit of the L-SIG isused as an indication indicating whether a frame is in a mode using anadditional data subcarrier.

Accordingly, a HEW device can interpret information of the additionaldata subcarrier when the indication of the L-SIG indicates the modeusing the additional data subcarrier.

Referring to FIG. 13, a data field includes a service field. The servicefield corresponds to the first 16 bits of the data field, and the first7 bits of the service field correspond to scrambler initialization bits.The scrambler initialization bits may be used to synchronize adescrambler and may be set to zero to enable estimation of an initialstate of a scrambler in a receiver. The remaining 9 bits are reservedand may be set to zero.

A scrambler of a transmitting device generates a scrambling sequence byrepeatedly generating a 127-bit sequence from a 7-bit scrambler seed.Accordingly, the scrambler seed is one-to-one mapped to the first 7 bitsof the scrambling sequence. Since the scrambler initialization bits areset to “0000000,” the first 7 bits of data that are outputted byscrambling the data field before being scrambled are equal to the first7 bits of the scrambling sequence. Therefore, a receiving device candetermine the first 7 bits of the data field in the received frame asthe scrambler seed and generate the same scrambling sequence as atransmitting device such that it can descramble the data field.

In some embodiments, a part of the first 7 bits in the scrambler seed,i.e., the scrambler sequence is used as an indication indicating whetheran additional data subcarrier is used. Since the first 7 bits of theservice field, i.e., the first 7 bits of the data field are equal to thefirst 7 bits of the scrambler sequence, the receiving device can detectwhether the additional data subcarrier is used based on the bit thatcorresponds to the indication among the first 7 bits of the data field.

In another embodiment, as shown in FIG. 14, a part of the reserved bitsof the service field may be used as the indication.

Referring to FIG. 15, in some embodiments, a receiving device maydetermine whether signaling information is transmitted by an additionaldata subcarrier, based on a power of a subcarrier corresponding to theadditional data subcarrier in a field to which the additional datasubcarrier is applied. Since the subcarrier corresponding to theadditional data subcarrier is used as a guard in the previous WLAN, thepower is not measured on that subcarrier. However, since the power ismeasured when the signaling information is transmitted by the additionaldata subcarrier, the receiving device can automatically detect a frameformat by measuring the power.

While a channel with a basic bandwidth (for example, a 20 MHz bandwidth)has been described above, an additional data subcarrier may be used in achannel with a multi-bandwidth. Hereinafter, these embodiments aredescribed with reference to FIG. 16 and FIG. 17.

FIG. 16 and FIG. 17 exemplify a frame format at a multi-bandwidth in awireless communication network according to other embodiments of thepresent invention. It is assumed in FIG. 16 and FIG. 17 that amulti-bandwidth is 40 MHz bandwidth for convenience.

Referring to FIG. 16, a request frame or response frame is transmittedby repeating the basic bandwidth (for example, a 20 MHz bandwidth). Thatis, each field of one basic bandwidth is duplicated to other basicbandwidth. Because a legacy device can interpret a frame of the basicbandwidth, the request frame or response frame that is transmitted byrepeating the basic bandwidth can maintain the compatibility with an HTdevice and a VHT device as well as the legacy device.

In some embodiments, data on an additional data subcarrier of one basicbandwidth are duplicated to an additional data subcarrier of other basicbandwidth.

In some embodiments, as shown in FIG. 17, a basic bandwidth may be notduplicated. In one embodiment, as described with reference to FIG. 10,signaling information that is different from signaling informationtransmitted by an additional data subcarrier of one basic bandwidth maybe transmitted by an additional data subcarrier of the other basicbandwidth. In another embodiment, as described with reference to FIG.11, a pattern may be defined by additional data subcarriers of aplurality of basic bandwidths. For example, when four additional datasubcarriers are used for each symbol in the 20 MHz bandwidth, 8×N matrixpatterns may be defined in 40 MHz bandwidth. In this case, since a lotof patterns can be defined, a large amount of information can betransmitted.

While it has been described in FIG. 16 and FIG. 17 that the 40 MHzbandwidth is one example of the multi-bandwidth, an additional datasubcarrier may be applied to a channel with the different bandwidth asdescribed with reference to FIG. 16 or FIG. 17.

Next, an example of signaling information to be transmitted by anadditional data subcarrier is described.

FIG. 18 shows an example of a channel width used in a wirelesscommunication network according to an embodiment of the presentinvention, and FIG. 19 and FIG. 20 are drawings explaining an exchangeof an RTS frame and a CTS frame in a wireless communication networkaccording to an embodiment of the present invention.

The previous WLAN supports contiguous channels but does not supportnon-contiguous channels when using a multi-bandwidth. For example, asshown in FIG. 18, an 80 MHz channel width in a VHT WLAN may be dividedinto a primary channel (primary) having a 20 MHz bandwidth (hereinafterreferred to as a “primary 20 MHz channel), a secondary channel(secondary 20) having a 20 MHz bandwidth (hereinafter referred to as a“secondary 20 MHz channel), and a secondary channel (secondary 40)having a 40 MHz bandwidth (hereinafter referred to as a “secondary 40MHz channel). A VHT device uses the primary 20 MHz channel for atransmission of the 20 MHz bandwidth, the primary 20 MHz channel and thesecondary 20 MHz channel for a transmission of the 40 MHz bandwidth, andthe primary 20 MHz channel, the secondary 20 MHz channel and thesecondary 40 MHz channel for a transmission of the 80 MHz bandwidth. Assuch, the VHT device uses a multi-channel by always using the otheradjacent secondary channel together with the primary 20 MHz channel.

However, in a wireless communication network according to an embodimentof the present invention, a HEW device can use the secondary channelindependently from the primary channel, and can divide and use thesecondary 40 MHz channel into 20 MHz bandwidths. For the independent useof the secondary channel, for example an orthogonal frequency divisionmultiple access (OFDMA) scheme may be used.

In this case, as shown in FIG. 19 and FIG. 20, when a transmittingdevice AP has data to be transmitted to a receiving device STA1, thetransmitting device AP transmits a request frame, for example an RTSframe, to notify this. It is assumed that the transmitting device APtransmits the data by using the primary 20 MHz channel (channel 1) and achannel (channel 40) with a 20 MHz bandwidth in the secondary 40 MHzchannel. For the compatibility with the previous WLAN that does notsupport the non-contiguous channels, the transmitting device APtransmits the RTS frame by duplicating an RTS frame of the 20 MHzbandwidth to the entire 80 MHz channel.

A device STA1 that corresponds to an address set to a receiver address(RA) field of the RTS frame transmits a response frame, for example aCTS frame, as a response of the RTS frame after an SIFS interval. Thereceiving device STA1 transmits the CTS frame by duplicating a CTS frameof the 20 MHz bandwidth to the entire 80 MHz channel. Further, thereceiving device STA1 transmits the CTS frame by copying an address setto a transmitter address (TA) of the RTS frame to an RA field of the CTSframe.

The transmitting device AP receiving the CTS frame transmits to thereceiving device STA1 a data frame on channels (for example, channel 1and channel 4) of assigned bandwidths data frame after the SIFSinterval. The device STA1 receiving the data frame transmits to thetransmitting device AP an ACK frame on channels (for example, channel 1and channel 4) of the assigned bandwidths after the SIFS interval.

In the previous WLAN, other device STA2 receiving the RTS frame updatesa NAV based on a duration field of the RTS frame, and other device STA3receiving the CTS frame updates a NAV based on a duration field of theCTS frame. Accordingly, the devices STA2 and STA3 cannot use the entire80 MHz channel in accordance with the NAV while the transmitting deviceAP and the receiving device STA1 exchange the data frame and the ACKframe.

In some embodiments, when the RTS frame and the CTS frame aretransmitted, an additional data subcarrier carries information on abandwidth which the device uses. Accordingly, when the devices STA2 andSTA3 are the HEW devices, they can interpret information carried by theadditional data subcarrier of the RTS frame or CTS frame, therebydetecting a bandwidth which the transmitting device AP and the receivingdevice STA1 do not use. Then, the devices STA2 and STA3 can transmit orreceive frames through channels (for example, channel 2 and channel 3)with bandwidths that are not used.

The legacy device, the HT device, or the VHT device cannot use theentire 80 MHz bandwidth because it cannot interpret the informationcarried by the additional data subcarrier.

As such, if information on the used bandwidth is provided through theadditional data subcarrier, frequency resources can be efficiently used.

In another embodiment, other signaling information may be transferred byan additional data subcarrier. The signaling information may include forexample at least part of frame type information, identifier relatedinformation, multi-user (MU) related information, transmission modeinformation such as OFDM or OFDMA, resource allocation information,power saving information, calibration information, dynamic clear channelassessment (CCA) information, and interference information. Theidentifier related information may include a BSS identifier (BSSID), apartial association identifier (PAID), and/or a group ID. Thecalibration information may include information for calibrating a power,timing, and/or a frequency. The signaling information may furtherinclude information associated with transmission or reception between atransmitting device and receiving device.

FIG. 21 is a flowchart exemplifying a frame transmitting method in adevice of a wireless communication network according to an embodiment ofthe present invention and FIG. 22 is a flowchart exemplifying a framereceiving method in a device of a wireless communication networkaccording to an embodiment of the present invention.

Referring to FIG. 21, a transmitting device generates a legacy shorttraining field (L-STF), a legacy long training field (L-LTF), a legacysignal field (L-SIG), and a data field of a legacy frame format totransmit a request frame or response frame (S211). The data fieldincludes a MAC frame part of the request frame or response frame. Thetransmitting device sets some of subcarriers that are not set as datasubcarriers in the legacy frame format as additional data subcarriers inat least part of the L-STF, the L-LTF, the L-SIG, and the data field(S212). Further, the transmitting device allocates information, forexample signaling information, to the additional data subcarriers(S213).

While the steps S211, S212, and S213 have been sequentially shown inFIG. 21, the steps S211, S212, and S213 may be performed in thedifferent order or at the same time.

Next, the transmitting device transmits a frame including the L-STF, theL-LTF, the L-SIG, the data field, and the information allocated to theadditional data subcarrier (S214).

Referring to FIG. 22, a receiving device receives a frame including alegacy short training field (L-STF), a legacy long training field(L-LTF), a legacy signal field (L-SIG), and a data field of a legacyframe format (S221). The data field includes a MAC frame part of therequest frame or response frame. The receiving device acquiresinformation, for example signaling information from additional datasubcarriers that are set by some of subcarriers which are not set asdata subcarriers in the legacy frame format, in at least part of theL-STF, the L-LTF, the L-SIG, and the data field (S222).

The receiving device may determine whether the receiving frame is in amode using an additional data subcarrier, based on an indicationincluded in a predetermined bit of the received frame. Alternatively,the receiving device may determine whether the receiving frame is in amode using an additional data subcarrier, by measuring a power ofsubcarriers that are not set as data subcarrier in the legacy frameformat.

A frame transmitting method and a frame receiving method according toabove embodiments of the present invention may be executed by a basebandprocessor 10 shown in FIG. 1 to FIG. 3. In one embodiment, instructionsfor executing the frame transmitting method and the frame receivingmethod according to above embodiments of the present invention may bestored in a recording medium such as a memory 40. In another embodiment,at least some of the instructions may be MAC software. In yet anotherembodiment, at least some of the instructions may be transmitted from arecording medium of a certain server and may be stored in the memory 40.

While this invention has been described in connection with what ispresently considered to be practical embodiments, it is to be understoodthat the invention is not limited to the disclosed embodiments, but, onthe contrary, is intended to cover various modifications and equivalentarrangements included within the spirit and scope of the appendedclaims. Further, two or more embodiments may be combined.

What is claimed is:
 1. An apparatus for facilitating wirelesscommunication, the apparatus comprising: a Radio Frequency (RF)transmitter; an antenna coupled to the RF transmitter; and a processorconfigured to transmit, using the RF transmitter and the antenna, afirst frame of a first format, the first frame including: a first set ofsymbols having a first number of subcarriers used for carrying a legacylong training field, including first training information for use inchannel estimation of a channel, and a second set of symbols having thefirst number of subcarriers for carrying a legacy signal field and asecond number of subcarriers for carrying second training informationfor use in channel estimation of the channel, wherein each subcarrier inthe second number of subcarriers includes a value of 1 or a value of −1based on a predetermined pattern, wherein each of the first and secondset of symbols includes, on a 20 MHz bandwidth basis of the first frame,a direct current subcarrier with an index of 0 and indices of the firstnumber of subcarriers are -26 through 26, excluding the index of thedirect current subcarrier, and indices of the second number ofsubcarriers are -28, -27, 27 and 28, and wherein the legacy signal fieldincludes one or more of rate and length information for describing aportion of the first frame.
 2. The apparatus of claim 1, wherein thefirst set of symbols includes subcarriers with indices of -28, -27, 27and 28 being used as guard tones.
 3. The apparatus of claim 1, whereinthe first set of symbols of the legacy long training field immediatelyprecede the second set of symbols of the legacy signal field in thefirst frame.
 4. The apparatus of claim 3, wherein a number of symbolsincluded in the second set of symbols is two.
 5. The apparatus of claim4, wherein a combined duration of the first set of symbols is identicalto a combined duration of the second set of symbols.
 6. The apparatus ofclaim 1, wherein the second number of subcarriers are present in eachsymbol of the second set of symbols.
 7. The apparatus of claim 1,wherein one half of the second number of subcarriers are locatedadjacent to one end of the first number of subcarriers, and the otherhalf of the second number of subcarriers are located adjacent to theother end of the first number subcarriers.
 8. The apparatus of claim 1,wherein the processor is further configured to transmit a second frameof a second frame format, wherein the second frame of the second formatuses the second number of subcarriers in the second set of symbols as aguard interval.
 9. The apparatus of claim 1, wherein a modulation andcoding scheme used for the first number of subcarriers is identical to amodulation and coding scheme used for the second number of subcarriers.10. An apparatus for facilitating wireless communication, the apparatuscomprising: a Radio Frequency (RF) receiver; an antenna coupled to theRF receiver; and a processor configured to receive, using the RFreceiver and the antenna, a first frame of a first format, the firstframe including: a first set of symbols having a first number ofsubcarriers used for carrying a legacy long training field, includingfirst training information for use in channel estimation of a channel,and a second set of symbols having the first number of subcarriers forcarrying a legacy signal field and a second number of subcarriers forcarrying second training information for use in channel estimation ofthe channel, wherein each subcarrier in the second number of subcarriersincludes a value of 1 or a value of −1 based on a predetermined pattern,wherein each of the first and second set of symbols includes, on a 20MHz bandwidth basis of the first frame, a direct current subcarrier withan index of 0 and indices of the first number of subcarriers are -26through 26, excluding the index of the direct current subcarrier, andindices of the second number of subcarriers are -28, -27, 27 and 28, andwherein the legacy signal field includes one or more of rate and lengthinformation for describing a portion of the first frame.
 11. Theapparatus of claim 10, wherein the first set of symbols includessubcarriers with indices of -28, -27, 27 and 28 being used as guardtones.
 12. The apparatus of claim 10, wherein the first set of symbolsof the legacy long training field immediately precede the second set ofsymbols of the legacy signal field in the first frame.
 13. The apparatusof claim 12, wherein a number of symbols included in the second set ofsymbols is two.
 14. The apparatus of claim 13, wherein a combinedduration of the first set of symbols is identical to a combined durationof the second set of symbols.
 15. The apparatus of claim 10, wherein thesecond number of subcarriers are present in each symbol of the secondset of symbols.
 16. The apparatus of claim 10, wherein one half of thesecond number of subcarriers are located adjacent to one end of thefirst number of subcarriers, and the other half of the second number ofsubcarriers are located adjacent to the other end of the first numbersubcarriers.
 17. The apparatus of claim 10, wherein the processor isfurther configured to transmit a second frame of a second frame format,wherein the second frame of the second format uses the second number ofsubcarriers in the second set of symbols as a guard interval.
 18. Theapparatus of claim 10, wherein a modulation and coding scheme used forthe first number of subcarriers is identical to a modulation and codingscheme used for the second number of subcarriers.
 19. A non-transitorycomputer-readable media comprising computer programming instructionsthat when executed by an apparatus, the apparatus including a processorand a Radio Frequency (RF) transmitter, cause the apparatus to:transmit, using the RF transmitter, a first frame of a first format, thefirst frame including: a first set of symbols having a first number ofsubcarriers used for carrying a legacy long training field, includingfirst training information for use in channel estimation of a channel,and a second set of symbols having the first number of subcarriers forcarrying a legacy signal field and a second number of subcarriers forcarrying second training information for use in channel estimation ofthe channel, wherein each subcarrier in the second number of subcarriersincludes a value of 1 or a value of −1 based on a predetermined pattern,wherein each of the first and second set of symbols includes, on a 20MHz bandwidth basis of the first frame, a direct current subcarrier withan index of 0 and indices of the first number of subcarriers are -26through 26, excluding the index of the direct current subcarrier, andindices of the second number of subcarriers are -28, -27, 27 and 28, andwherein the legacy signal field includes one or more of rate and lengthinformation for describing a portion of the first frame.
 20. Thenon-transitory computer-readable media of claim 19, wherein the firstset of symbols includes subcarriers with indices of -28, -27, 27 and 28being used as guard tones.